In recent years, a solid-state scanning type LED (Light Emitting Diode) copy machine having an exposure optical system using a semiconductor light emitting element as a light source has been widely used. The exposure device, which forms an electrostatic latent image on a surface of a photoconductive drum of the LED copy machine, has a lens mirror array that refracts and reflects light based on an image signal incident from the light source to converge it on the surface of the photoconductive drum. For example, the lens mirror array has a plurality of optical elements for converging light from the plurality of light sources arranged in a main scanning direction on the surface of the photoconductive drum. The lens mirror array is made of, for example, a transparent resin, and has a structure in which the plurality of optical elements is integrally connected to each other in the main scanning direction. A light shielding material for cutting out noise light unnecessary for exposure (for example, light undesirably incident on an adjacent optical element) is applied to a surface of each optical element.
In addition, a lens array element in which a prism structure is arranged around a lens on a light emitting surface on which the lens is formed is provided as a module for cutting out the noise light included in the light incident on the lens. The prism structure reflects the noise light according to a retroreflection principle.